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Introduction to the Three Gorges Dam
The largest dam ever built in China is the Three Gorges Dam. The three Gorges Dam locates in Sandouping Town, Yichang City, Hubei Province, China, which is the easternmost section of the Three Gorges Reservoir. The distance between the Three Gorges Dam and the Gezhouba Water Conservancy Project is 38 km.

The body and the diversion section are two main blocks of the Three Gorges Dam. The two constitute a 3335 meters length and 185 meters high world-renowned flood control project The Chinese government invested a total of 95.46 billion yuan in this project. The construction was made an officially public appearance on December 14, 1994 and May 20, 2006. The entire line was successfully constructed.

The power generation role of the Three Gorges Dam
The Three Gorges Hydropower Station has a total installed capacity of 22.5 million kilowatts and an annual power generation capacity of about 100 billion kWh. The Three Gorges Power Plant had produced 704.5 billion kilowatt-hours of electricity, generating 183.1 billion yuan in sales revenue, and the Three Gorges Project had recovered its investment costs as of November 30, 2013. After the 26 units are put into operation, the annual power generating capacity will be 84.7 billion kWh, which will reduce coal consumption by 40-50 million tonnes per year, reduce sulphur dioxide emissions by 2 million tonnes, carbon monoxide emissions by 10,000 tonnes, and industrial wastewater by a considerable amount, and recover the cost of 25 billion yuan. It was once thought that once the Three Gorges Hydropower Station was completed, its high power generation capacity would result in an oversupply of electricity. However, even if the Three Gorges Hydropower Station is completed, its installed capacity will only be marginally higher than 2% of China's total installed capacity by that time, and it will have little effect on China's power supply and demand situation. Furthermore, China has had extreme power supply shortages since 2003, coal prices have risen, and the Three Gorges units have begun producing electricity at the appropriate time. Power production has met the predetermined plan in the first two years of service, but supply is still in short supply. Some people were concerned at first that the Three Gorges hydropower project would interrupt the power grid and create waste. As a result, they continued to miscalculate the trajectory of history. China's electricity demand is increasing at the same rate as the country's economic growth, and the Three Gorges Hydropower Station has helped to alleviate the country's electricity shortage. Per year, the Three Gorges produces more than 100 billion kWh of electricity.

The function flood control
In 1954, the Yangtze River flooded, the water level in Shashi was 44.38m, the Jingjiang flood diversion area was opened, and 200,000 people became homeless. After the flood diversion, the water level of Shashi Station dropped by 0.96m, and another 0.76m. The water level limit of Shashi Station is 45m. In 1998, the Yangtze River flooded. The water level in Shashi risen to 44.68m on August 6. The central government enacted an order to prepare for flood diversion (In 1986, the State Council Order No. 76 required that when the Shashi water level reached 44.67 meters, the forecast will continue to rise. The north gate of the Jingjiang flood diversion area, at that time, was opened from 6000 cubic meters per second to 7,700 cubic meters per second) at 12am on the same day. Nearly 335,000 people in the flood diversion area began to be transferred. At 2am on August 7, the embankment of Mengxi Dadi burst. At 11am on the 7th, the water level in Shashi was 44.98m. The fifth flood peak passed Yichang on the same day, with a flow rate of 63,200 cubic meters per second. At 4am on August 8, the water level in Shashi was 44.95m; on August 16, the sixth flood peak, Yichang flow was 63,300 cubic meters per second, and the water level in Shashi was 45.22m on the same day. , The flood diversion area is still not activated. The flood has overflowed the embankment, and the PLA is relying on sandbags to resist it. Fortunately, after this, there will be no greater peaks. Later, in 2002, the Three Gorges was impounded. On July 19, 2010, the flood flow into the Three Gorges Reservoir reached 69,000 cubic meters per second, exceeding the largest flood peak in 1998, and the downstream was unharmed. On July 24, 2012, the flood flow into the Three Gorges Reservoir reached 68,500 cubic meters per second, exceeding the largest flood peak in 1998, and the downstream was unharmed. In fact, since the impoundment of the Three Gorges, there have been more than two major floods with a single peak exceeding the largest peak in 1998, but no one has heard about the critical situation of the Jingjiang section in the news. No news is good news. And this is all thanks to the Three Gorges. According to statistics, during the Yangtze River flood in July 2012, “the Three Gorges Reservoir’s speak-shaving operation will resolve high flood levels into medium-to-high floods, with a general decrease of 0.6 to 2 meters.” The discharge flow was maintained at 38,000 to 45,000 cubic meters. "Every second", the number of people on the embankment decreased by 320,000. The improvement over the same period in July 1998 is not one and a half.

Impact on biology
The impact on biology is the part of the nature. The organisms in the Yangtze River Basin is mainly reflected in the following two aspects: 1. The impact of water storage in the wet season on fish reproduction. The principle of the dam is to store water in the wet season and then release in the dry season. Water power generation. The wet season is from May to September of the year, and there is not much natural water in the remaining months, and the water resources in the wet season from May to September can be used. Therefore, in the past few months, the reservoir will release as little water as possible and generate more electricity. The natural reproduction of fish also happens to be spring and summer when the temperature is suitable, which happens to be the wet season. Many fish live and breed in different waters. They will rush to a special place to mate during the breeding season, and then return to the waters where they usually live (this phenomenon is called fish migratory). The interception effect of the reservoir on the water body prevents the fish from passing through the reservoir to reach the waters where they multiply, which destroys the law of fish multiplication. 2. The temperature of the water discharged from the reservoir has a very obvious effect on the reproduction of fish. The density of the water changes with the change of temperature, and the water density at 4°C is the highest. This also determines that the water body of the reservoir has a characteristic of temperature stratification. The surface water body is closer to the temperature, while the temperature of the bottom water body is close to zero degrees. The discharge location of the reservoir is often in the middle and lower part of the dam, which leads to a lower temperature of the discharged water and lower water temperature of the downstream river. A few years ago, there was news that people in Wuhan discovered that the river water was getting cold when the Three Gorges was released. When the river water temperature drops suddenly, it will also have many impacts on the survival of fish.

Impact on soil and water conservation
The impact of the issue of soil and water conservation. When the normal water level of the Three Gorges Reservoir is 175 meters, 360,000 mu of arable land and garden land will be submerged; the relocation of cities, counties, market towns, rural residential areas, industrial and mining enterprises, and roads and other professional projects in the resettlement area will also occupy nearly 7 square meters. Ten thousand mu of farmland. This may cause large-scale destruction of forests and land reclamation, planting on steep slopes, new soil erosion, deterioration of the living environment, and difficulties for the further economic development of the reservoir area.

Impact on geological
After the Three Gorges Reservoir is impounded, some unstable collapsed bodies and landslides will slide into the Yangtze River, and some will threaten the safety of local people's lives and property. How to treat some of the predicted unstable collapsed bodies and landslides before the impoundment of the Three Gorges Reservoir is the third problem that needs to be solved urgently.

Impact on sediment
During the design of the Three Gorges Project, some people raised concerns that Chongqing would become a “dead port” due to sedimentation after the water was stored, and the decrease in the amount of sediment in the downstream would reduce the source of nutrients for organisms, and the riverbed of the Jingjiang section would change. Deep, causing bank collapse, and even causing seawater recharge in Shanghai. At present, it is necessary to observe and study the impact of water storage on the upstream and downstream rivers and find solutions.

Impact on water pollution
Water pollution in some river sections in the reservoir area has increased. Before the completion of the Three Gorges Project, water pollution in some sections of the reservoir area was already very serious. After the Three Gorges Reservoir is impounded, especially in winter, the upstream water flow will decrease, the flow velocity of the water body in the reservoir will slow down, and the self-purification capacity of the water body will decrease. If various sources of pollution are not treated in time, a large amount of industrial wastewater and domestic sewage will still be discharged into the Yangtze River. Water pollution in the river section is bound to aggravate further, and even threaten the water source of urban domestic water.Up to now, the state has allocated 4 billion yuan to build more than ten sewage treatment plants in upstream areas. If they operate normally, water pollution can be eliminated to a large extent. What needs to be done at present is to strengthen supervision and ensure the normal operation of sewage treatment plants run.

References List:
The Three Gorges Dam: an ecological perspective. Frontiers in Ecology and the Environment, Jianguo Wu, Jianhui Huang, Xingguo Han, Xianming Gao, Fangliang He, Mingxi Jiang, Zhigang Jiang, Richard B. Primack, Zehao Shen (June,2004).

Reservoir resettlement in China: past experience and the Three Gorges Dam. The Geography Journal, Li Heming, Paul Waley, Phil Rees (September 2001)

Three Gorges Dam Project, Yangtze River, China, Peter H. Gleick (2009)

Three Gorges Project: Efforts and challenges for the environment, Bo-Jie Fu, Bing-Fang Wu, Yi-He Lü

Three-Gorges Dam--Experiment in Habitat Fragmentation? Jianguo Wu, Jianhui Huang, Xingguo Han, Zongqiang Xie, Xianming GaoThree-Gorges Dam--Experiment in Habitat Fragmentation?